1. Field of the Invention
The present invention relates to back-up electrical power supplies for electrical equipment.
More specifically, the invention relates to back-up supplies for electrically powered devices which require a continuous electrical supply (at least in some applications).
2. Description of the Prior Art
There are many examples of such devices. For example, electrical memories and other devices may be of volatile form, that is, they rely on a sustained supply of power to prevent the loss of any data which is stored or any function which is enabled. Thus in the event of a power failure the contents of the memory and the function of the device will be lost.
It has been proposed to provide a back-up power supply for such memories and devices. In one case in which a back-up power supply for a memory is provided, the back-up power supply is mounted on the same circuit board as that into which the memory is plugged and furthermore additional circuitry is mounted on that circuit board to sense the failure of the power supply and to switch the back-up power supply in instead.
This arrangement is relatively inconvenient and inflexible. Plug-in memory modules allow such modules to be relatively easily interchanged. However, this cannot be done without loss of the contents of the memory except by interchanging circuit boards provided with back-up power supplies.
This tends to be expensive and may not be possible where the circuit boards in question are incompatible.
It is an object of the invention to provide an improved back-up electrical power supply.